KRAS mutations are a major risk factor in colorectal cancers. In particular, a point mutation of KRAS of amino acid 12, such as KRASV12, renders it stable activity in oncogenesis. We found that krasV12 promotes intestinal carcinogenesis by generating a transgenic zebrafish line with inducible krasV12 expression in the intestine, Tg(ifabp:EGFP-krasV12). The transgenic fish generated exhibited significant increases in the rates of intestinal epithelial outgrowth, proliferation, and cross talk in the active Ras signaling pathway involving in epithelial-mesenchymal transition (EMT). These results provide in vivo evidence of Ras pathway activation via krasV12 overexpression. Long-term transgenic expression of krasV12 resulted in enteritis, epithelial hyperplasia, and tubular adenoma in adult fish. This was accompanied by increased levels of the signaling proteins p-Erk and p-Akt and by downregulation of the EMT marker E-cadherin. Furthermore, we also observed a synergistic effect of krasV12 expression and dextran sodium sulfate treatment to enhance intestinal tumor in zebrafish. Our results demonstrate that krasV12 overexpression induces intestinal tumorigenesis in zebrafish, which mimics intestinal tumor formation in humans. Thus, our transgenic zebrafish may provide a valuable in vivo platform that can be used to investigate tumor initiation and anticancer drugs for gastrointestinal cancers.

Intestinal carcinogenesis is a multistep process that begins with epithelial hyperplasia, followed by a transition to an adenoma and then to a carcinoma. Many etiological factors, including KRAS mutations and inflammation, have been implicated in oncogenesis. However, the potential synergistic effects between KRAS mutations and inflammation as well as the potential mechanisms by which they promote intestinal carcinogenesis remain unclear. Thus, the objective of this study was to investigate the synergistic effects of krasV12, lipopolysaccharides (LPS), and/or dextran sulfate sodium (DSS) on inflammation, tumor progression, and intestinal disorders using transgenic adults and larvae of zebrafish. Histopathology and pathological staining were used to examine the intestines of krasV12 transgenic zebrafish treated with LPS and/or DSS. LPS and/or DSS treatment enhanced intestinal inflammation in krasV12 transgenic larvae with concomitant increases in the number of neutrophils and macrophages in the intestines. The expression of krasV12, combined with LPS treatment, also enhanced epithelial hyperplasia and tubular adenoma, demonstrated by histopathological examinations and by increases in cell apoptosis, cell proliferation, and downstream signaling of phosphorylated AKT serine/threonine kinase 1 (AKT), extracellular-signal-regulated kinase (ERK), and histone. We also found that krasV12 expression, combined with LPS treatment, significantly enhanced changes in intestinal morphology, specifically (1) decreases in goblet cell number, goblet cell size, villi height, and intervilli space, as well as (2) increases in villi width and smooth muscle thickness. Moreover, krasV12 transgenic larvae cotreated with DSS and LPS exhibited exacerbated intestinal inflammation. Cotreatment with DSS and LPS in krasV12-expressing transgenic adult zebrafish also enhanced epithelial hyperplasia and tubular adenoma, compared with wild-type fish that received the same cotreatment. In conclusion, our data suggest that krasV12 expression, combined with LPS and/or DSS treatment, can enhance intestinal tumor progression by activating the phosphatidylinositol-3-kinase (PI3K)/AKT signaling pathway and may provide a valuable in vivo platform to investigate tumor initiation and antitumor drugs for gastrointestinal cancers.